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WO2001061328A2 - Capteur electrochimique - Google Patents

Capteur electrochimique Download PDF

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Publication number
WO2001061328A2
WO2001061328A2 PCT/DE2001/000641 DE0100641W WO0161328A2 WO 2001061328 A2 WO2001061328 A2 WO 2001061328A2 DE 0100641 W DE0100641 W DE 0100641W WO 0161328 A2 WO0161328 A2 WO 0161328A2
Authority
WO
WIPO (PCT)
Prior art keywords
channel
sensor according
doped
diamond
partially
Prior art date
Application number
PCT/DE2001/000641
Other languages
German (de)
English (en)
Other versions
WO2001061328A3 (fr
Inventor
Erhard Kohn
Andrej Denisenko
Aleksandar Aleksov
Original Assignee
Erhard Kohn
Andrej Denisenko
Aleksandar Aleksov
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Erhard Kohn, Andrej Denisenko, Aleksandar Aleksov filed Critical Erhard Kohn
Priority to AU39187/01A priority Critical patent/AU3918701A/en
Priority to DE10190529T priority patent/DE10190529D2/de
Publication of WO2001061328A2 publication Critical patent/WO2001061328A2/fr
Publication of WO2001061328A3 publication Critical patent/WO2001061328A3/fr

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
    • G01N27/02—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance
    • G01N27/04—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating resistance
    • G01N27/041—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating resistance of a solid body

Definitions

  • the present invention relates to a sensor for detecting electrochemical potentials of a sample, for example a liquid.
  • electrochemical sensors are used in particular as pH electrodes.
  • the object of the present invention is to provide an electrochemical sensor for electrochemical tial of a sample, for example liquids, with which electrochemical potentials can be measured easily, safely and stably.
  • the electrochemical sensor according to the invention consists of an insulating substrate on which a conductive semiconductor channel is arranged.
  • This semiconductor channel must consist of an electrically conductively doped semiconductor which has a high band gap and an unpinned surface potential.
  • a semiconductor surface with unpinned surface potential is characterized in that the density of the surface states is so low that it is ensured that the barrier height of the Schottky contact depends on the metal work function.
  • S.M. Sze "Physics of Semiconductor Devices," J Wiley, NY 1981, p. 868 referenced.
  • the channel is electrically contacted by two contacts in order to record the conductivity of the channel as a measured value.
  • Diamond, gallium nitride or aluminum nitride can be used as semiconductor materials.
  • Gallium nitride and aluminum nitride have an unpinned surface potential on the surface and are largely chemically inert, in particular. These materials can therefore be brought into direct contact with the sample to be measured.
  • Doped diamond is available as a further material, conductivity being generated in the diamond by doping, for example with boron. Such Doping is stable and does not depend on external influences.
  • the diamond is then terminated with hydrogen on its surface facing the measurement solution in order to stably maintain an unpinned surface potential.
  • the conductivity can be generated with boron, lithium, silicon or magnesium doping. It is important in the present electrochemical sensor that this conductivity is generated in a stable manner.
  • semiconductors with a wide band gap are suitable for chemical sensors since they are not chemically attacked.
  • Diamond is particularly suitable among these semiconductor materials.
  • the large band gap enables a large potential window with regard to the stability towards water, which comes close to the 5.5 eV band gap for high-quality CVD diamond films.
  • This high chemical stability of the diamond surface enables the successful realization of diamond electrochemical electrodes
  • the electrochemical potential in the electrochemical sensors according to the invention, when in contact with a chemical, for example in a solution, the corresponding electrochemical potential now occurs at the interface between the channel and the chemical. This changes the surface potential of the channel and thus the depletion of the channel or the channel conductivity. So the electrochemical potential can be detected in a simple and safe manner.
  • the sensors are produced from thin layers of semiconductors with a high band gap. These layers are grown heteroepitaxially on various substrates.
  • the conductive channel can be doped in situ by adding the dopants to the reaction chamber.
  • the alternative method for doping the channel is ion implantation.
  • diamond can be p-doped with boron
  • GaN can be n-doped with Si
  • GaN can be p-doped with Mg.
  • the state of the free surface with the detached Fermi level can, if necessary, be achieved by certain surface treatments, such as play through plasma treatment.
  • a free surface with a detached Fermi level is observed in diamond after treatment in hydrogen plasma and cooling in a hydrogen atmosphere.
  • the state of the surface with the Fermi level removed can be observed directly after crystal growth.
  • FIG. 1 shows a schematic cross section of an FET structure without a control electrode
  • FIG. 3 shows the pH dependence of the surface resistance of the FET structure from FIG. 2;
  • 5 shows the pH response of a boron-doped diamond channel (a) untreated, b) after hydrogen plasma treatment); 6 shows a schematic representation of the pH detection with a diamond surface;
  • Reference numeral 1 shows a schematic cross section of the FET structure without a control electrode.
  • Reference numeral 1 denotes a type Ib diamond substrate, reference numeral 2 a boron-doped surface channel with a charge carrier density N A of 10 20 cm "3 and one
  • the p-type surface channel 2 was produced on polished surfaces (3x3 mm 2 ) of a synthetic nitrogen-doped diamond substrate 1. The lattice structure corresponded to a [100] orientation. The resistance of the diamond substrate 1 at room temperature was in the g- ⁇ -cm range. After the surface channel 2 had been produced, the ohm 'contacts 3 were produced by completely metallizing the entire surface with gold.
  • the diamond crystals together with two metallic pads (pads) for external contacting, were applied to a dielectric carrier.
  • the surface channel 2 was connected to the pads via thin wires 5, which were fastened with a silver paste.
  • the width of the open area was about 500 ⁇ m, while the length corresponded to that of the substrate (3 mm).
  • the epitaxy of the boron-doped p-conducting channel 2 was carried out in a MWCVD reactor.
  • the doping was carried out with a fixed boron doping source, according to a method which is also used for the production of channels of a FET structure from ⁇ -boron-doped diamond.
  • boron doping profiles with a layer thickness of 2 to 4 nm can be realized, the layer thickness being able to be determined with electron recoil detection (ERD).
  • ELD electron recoil detection
  • the sample was cooled in vacuo to avoid complete saturation of the surfaces with hydrogen atoms.
  • the channels of the pH sensors produced in this way showed an activation energy of the conductivity of approximately 5 eV. This low activation energy corresponds to a degree of doping of approximately 10 20 cm "3.
  • the surface area density in the surface channel was between 1 and 3-10 13 cm " 2 .
  • the resistance at room temperature of the channel produced was in the K ⁇ D _1 range.
  • the boron-doped channel with a surface termination 7 with hydrogen was carried out by treatment with a hydrogen plasma in a CVD reactor (duration 60 min). Such treatment presumably leads to a complete saturation of the carbon bonds on the surface with hydrogen atoms.
  • the temperature of the sample holder was 400 ° C.
  • a negative bias of -50 V was applied to the sample holder. No significant fluctuations in the channel resistance were observed after the treatment.
  • an argon / oxygen plasma was used to produce a boron-doped diamond channel 2 with a surface termination 7 with oxygen (duration 2 min at room temperature (RT)).
  • RT room temperature
  • the surface of the diamond exhibits a number of different states, resulting in a Fermi level of the surface of approximately 1.7 eV above the valence band.
  • the influence of the surface termination with oxygen could be observed on the basis of the increase in the resistance of the boron-doped channel from 5 to approximately 180 K- ⁇ -D "1 .
  • the pH measurements were carried out at room temperature (RT) with buffered acidic and basic aqueous solutions (pH between 1 and 13).
  • FIG. 2 shows the IV characteristic of an FET structure without a control electrode with a boron-doped diamond surface channel.
  • 3 shows the pH dependence of the surface resistance.
  • the dotted curve shows the expected pH dependence with regard to the thermodynamic equilibrium between the p-type diamond and liquid solutions.
  • the two arrows drawn in the figure indicate the reproducibility of the measured pH dependency when it is determined from low to high pH or vice versa.
  • the sensor works similar to an FET when operating in the depletion phase. From this it can be seen that the surface channel of the diamond pH sensor is affected by the pH-dependent threshold potential The interface between liquid and diamond is also poorer compared to a surface exposed to air. It should be noted that only the conductivity of the structures produced in this way was used as the reference value for the pH dependence in the corresponding figures. After contact with the liquid solution, the conductivity of the dried surface sometimes differed from the original value, depending on which cleaning method was used. The conductivity usually returned to its original value after cleaning the sample with distilled water.
  • the pH dependency was reproducible at low bias voltages if the current was stabilized for 10 to 15 s after immersing the sensor in the solution. However, a strong increase in the current was observed with a bias voltage above 5-6 V, which indicated the occurrence of a leakage current m the liquid solution. In this case the resistance of the structure was substantially less than the channel resistance measured in air.
  • the leakage current observed was consistent with the formation of hydrogen and oxygen on the diamond surface, which indicates a hydrolysis.
  • the leakage current occurred when a potential drop between the source and the sink occurred across the interface between the liquid and diamond m of the order of magnitude of the potential of the band gap, which indicates a chemically induced band gap of this order of magnitude of the material.
  • the channel was gradually increased by increasing the pH taking the conductivity into account
  • FIG. 5b can thus be explained from an increased density of ionic radicals which are bound to the C-H bonds lying on the surface.
  • Fig. 6 shows a schematic representation of the mechanism of a pH measurement with a diamond surface. The model has only a pictorial meaning, since it is currently not possible to prove which surface bonds are responsible for determining the Fermi level and what the curvature of the surface band looks like in the presence of adsorbed radicals.
  • Fig. 5 shows that the extrapolation of the pH dependence, both for channels with surface termination with and without hydrogen
  • the sensitivity to ionic solutions and their pH values could be demonstrated for the first time with an FET structure without a control electrode (gate).
  • the conductive surface channel is in direct contact with the liquid solution, which acts as a liquid control electrode.
  • Two different types of p-type surface channels were examined as shown above:
  • the pH response for diamond as a channel semiconductor material of the sensors is greatly influenced by the surface termination.
  • the channel became increasingly poor with increasing pH.
  • the tendency in the depletion of the channel shows that this effect is determined by the adsorption of ionic radicals (eg OH " ) and their influence on the CH dipoles on the surface.
  • ionic radicals eg OH "
  • the sensors correspond completely to those in FIG. 1, but the channel consists of GaN, the surface of which has no hydrogen termination 7.
  • a GaN layer was applied to a sapphire substrate. This GaN channel had an n-type defect conductivity. 8 shows the measured values for two such structures with different channel thicknesses t of 0.9 ⁇ m and 1.3 ⁇ m.
  • the n-type GaN channel of both sensors shows an increasing depletion with increasing pH value. It can also be seen from this that surfaces of channel materials which have a sufficiently high band gap and have an unpinned surface potential, such as, for example GaN or A1N are suitable for electrochemical sensors according to the invention. If these materials are used, it is not necessary to modify the measuring surface that comes into contact with the solution to be measured. It can therefore be measured directly with the GaN or AIN surface.

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  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • Physics & Mathematics (AREA)
  • Health & Medical Sciences (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Analytical Chemistry (AREA)
  • Biochemistry (AREA)
  • General Health & Medical Sciences (AREA)
  • General Physics & Mathematics (AREA)
  • Immunology (AREA)
  • Pathology (AREA)
  • Investigating Or Analyzing Materials By The Use Of Electric Means (AREA)

Abstract

La présente invention concerne un capteur électrochimique destiné au potentiel électrochimique d'un échantillon, en particulier de liquides. Dans ce capteur, un canal conducteur constitué d'un semi-conducteur dopé de manière à conduire l'électricité, ayant une largeur de bande interdite élevée et un potentiel de surface régulier, se trouve sur un substrat isolant. Deux contacts servent au contact électrique avec le canal semi-conducteur de l'extérieur.
PCT/DE2001/000641 2000-02-18 2001-02-19 Capteur electrochimique WO2001061328A2 (fr)

Priority Applications (2)

Application Number Priority Date Filing Date Title
AU39187/01A AU3918701A (en) 2000-02-18 2001-02-19 Electrochemical sensor
DE10190529T DE10190529D2 (de) 2000-02-18 2001-02-19 Elektrochemischer Sensor

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
DE10007525.8 2000-02-18
DE2000107525 DE10007525A1 (de) 2000-02-18 2000-02-18 ph-Sensoren auf Halbleitern mit hohem Bandabstand

Publications (2)

Publication Number Publication Date
WO2001061328A2 true WO2001061328A2 (fr) 2001-08-23
WO2001061328A3 WO2001061328A3 (fr) 2002-03-14

Family

ID=7631497

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/DE2001/000641 WO2001061328A2 (fr) 2000-02-18 2001-02-19 Capteur electrochimique

Country Status (3)

Country Link
AU (1) AU3918701A (fr)
DE (2) DE10007525A1 (fr)
WO (1) WO2001061328A2 (fr)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN108780060A (zh) * 2016-03-02 2018-11-09 学校法人早稻田大学 离子传感器、离子浓度测定方法、以及电子部件

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE102007039706A1 (de) 2007-08-22 2009-02-26 Erhard Prof. Dr.-Ing. Kohn Chemischer Sensor auf Diamantschichten
US10634654B2 (en) * 2016-12-29 2020-04-28 City University Of Hong Kong Electrochemical detector

Family Cites Families (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4020830A (en) * 1975-03-12 1977-05-03 The University Of Utah Selective chemical sensitive FET transducers
FR2510260A1 (fr) * 1981-07-24 1983-01-28 Suisse Fond Rech Microtech Dispositif semiconducteur sensible aux ions
US5362975A (en) * 1992-09-02 1994-11-08 Kobe Steel Usa Diamond-based chemical sensors
DE19981016D2 (de) * 1998-06-04 2001-05-10 Gfd Ges Fuer Diamantprodukte M Diamantbauelement mit Rückseitenkontaktierung und Verfahren zu seiner Herstellung

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN108780060A (zh) * 2016-03-02 2018-11-09 学校法人早稻田大学 离子传感器、离子浓度测定方法、以及电子部件
US10845323B2 (en) * 2016-03-02 2020-11-24 Waseda University Ion sensor, ion concentration measurement method, and electronic component
CN108780060B (zh) * 2016-03-02 2021-11-09 学校法人早稻田大学 离子传感器以及离子浓度测定方法

Also Published As

Publication number Publication date
DE10007525A1 (de) 2001-09-06
WO2001061328A3 (fr) 2002-03-14
AU3918701A (en) 2001-08-27
DE10190529D2 (de) 2002-10-10

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